Limitations of cylindrical carbon nanotubes based on the buckminsterfullerene structure as delivery vehicles for therapeutic agents include their chemical inertness, sharp edges, and toxicological concerns (Bianco et al. 2005; Kam and Dai 2005; Singh et al. 2005; Bhirde et al. 2009; Li, R. et al. 2010; Warheit et al. 2004; Shvedova et al. 2003; Kisin 2007; Murray et al. 2009; Smart et al. 2006; Belyanskaya et al. 2009; Magrez et al. 2006; Poland et al. 2008). Nanotubes can also be formed from polymeric materials such as polyelectrolytes (Ai et al. 2003), collagen (Landoulsi et al. 2009) and poly(3,4-ethylenedioxythiophene) (Xiao et al. 2007) via template synthesis using nanoporous membranes containing arrays of aligned cylindrical pores (Martin 1994; Huczko 2000). This approach produces either polymer-functionalized nanoporous membranes or polymer-based nanotubes from a sacrificial template (Martin 1996). The development of polymer nanotubes holds many promises for biomedical and biotechnological applications because of their greater biocompatibility (Duncan 2003; Martin and Kohli 2003). However, the inability of synthesized polymer-based nanotubes to maintain their shape limits commercial applications (Reiner et al. 2006, Mabrouk et al. 2009).
Lignin is a complex phenolic plant cell wall polymer formed by the oxidative coupling of hydroxycinnamyl alcohols and related compounds (Ralph et al. 2004). It can be synthesized in vitro (Nimz and Ludeman, 1976; Higuchi et al. 1994; Grabber et al. 1995; Terashima et al. 1996). Lignin is a waste product from paper mills and biorefineries that convert renewable resources, such as lignocellulosic biomass, into fuels and chemicals (Ragauskas et al. 2006). The desire to reduce both the dependency on imported fossil fuels and the net emission of greenhouse gasses attracts attention to the potential for bio-based fuels and chemicals. Since the presence of lignin in the biomass lowers the processing efficiency (Yang and Wyman, 2004; Chen and Dixon 2007), lignin is typically removed during a thermo-chemical pretreatment (Mosier et al. 2005) and burned to generate heat for the distillation of alcoholic fuels from the fermentation broth. Lignin's rich diversity in chemical bonds and functional groups may, however, be attractive for applications that require biodegradability, biocompatibility, and low cost.